Centrifuges

ABSTRACT

An analytical centrifuge to receive a plurality of different rotors each carrying a track with a segment having a light reflective property distinct from adjacent regions of the track and having a length along the track which is related to the maximum desired speed of the rotor, the centrifuge having optical sensing means for sensing said segment and a time comparator for comparing the duration of the signal obtained by the sensing means in each rotor revolution with a fixed time to sense when the maximum desired speed is reached. Analytical rotors also carry a further track having distinct segments corresponding to respective compartments of the rotor and which are optically sensed to provide in conjunction with the signal obtained from the first-mentioned segment gating signals for examining selectable compartments of the rotor one-by-one.

United States Patent [191 Olliffe CENTRIFUGES 21 Appl. No.: 61,602

[52] US. Cl. 318/313 [51] Int. Cl. H02p 5/16 [58] Field of Search250/217, 218; 233/26;

[56] References Cited UNITED STATES PATENTS 8/1969 Waye ..318/327 6/1971Badessa ..3l8/327 Primary ExaminerRobert K. Schaefer Ass st n Er m ne.Ih9n as,Langr o. V, Attorney, Agent, or FirmWaters, Roditi, Schwartz &Nissen Aug. 27, 1974 [57 ABSTRACT An analytical centrifuge-to receive aplurality of different rotors each carrying a track with a segmenthaving a light reflective property distinct from adjacent regions of thetrack and having a length along the track which is related to themaximum desired speed of the rotor, the centrifuge having opticalsensing means for sensing said segment and a time comparator forcomparing the duration of the signal obtained by the sensing means ineach rotor revolution with a fixed time to sense when the maximumdesired speed is reached. Analytical rotors also carry a further trackhaving distinct segments corresponding to respective compartments of therotor and which are optically sensed to provide in conjunction with thesignal obtained from the first-mentioned segment gating signals forexamining selectable compartments of the rotor one-by-one.

4 Claims, 9 Drawing Figures FIGSci. A

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PATENTEDAuczmm SHEEI u or 5 FIGS.

CENTRIFUGES BACKGROUND OF INVENTION This invention relates tocentrifuges, and is particularly applicable to analytical centrifuges,i.e., centrifuges having an optical or other radiation system forsensing the radiation absorption properties of material whilst it isbeing centrifuged.

Modern centrifuges have the requirement that they should be operablewith a variety of rotors of different types and ratings. Each rotor hasits own maximum permissible speed rating to avoid overspeed and damageto the rotor. In the past, mechanical systems have been employed tosense the speed rating and effect some corresponding limitation upon amotor speed control circuit whereby an operator will be overriden'should he select too high a speed. In more modern systems a more directmethod is employed wherein maximum permissible speed of the rotor isdirectly sensed, when it occurs. In practice, each rotor is providedwith a plurality of distinct portions directly related in number withthe maximum permissible speed. These portions are sensed optically ormagnetically to create an electrical signal with a frequencyproportional to actual rotor speed and to the speed rating. This signalis compared with a fixed frequency, and when equality is sensed, it isknown that the rotor has reached its speed rating. However, this systemoperates in steps, i.e., with a given fixed frequency, there are onlycertain speed ratings which can be sensed. The sizes of these steps aresignificant in modern high speed centrifuges, where each rotor canaccommodate only a limited number of portions, e.g., 5 to 15.

It is an object of the present invention to provide the possibility of acontinuous range of speed ratings.

SUMMARY OF INVENTION This object is achieved according to one aspect ofthe invention in that each rotor has a predetermined maximum speed ofrotation defined by the length along an arcuate path around the rotoraxis of a surface portion carried by the rotor, the centrifuge havingsensing means for sensing said surface portion without contact therewithso as to produce a signal with a time duration which is a function ofsaid length, and means responsive to the time duration of said signal toprevent increase in the speed of operation of the centrifuge when thetime duration of said signal falls to a predetermined value.

It will be seen that said predetermined value may be preset so that itis equal to the duration of said signal when the rotor has reached apermissible maximum speed of rotation. In that case the length of saidsection, i.e., the angle it subtends at the axis, will be directlyproportional to the desired maximum speed of the rotor.

Preferably the surface portion has a radiation affecting propertydifferent from that of adjacent surface portions on said arcuate pathand the centrifuge has radiation directing or generating means fordirecting radiation at the path, the sensing means being radiationsensitive means for receiving radiation from the path and originatingfrom the directing means. Thus, optical radiation may be employed.

The above aspect of the invention is applicable generally to all typesof centrifuge rotors, including analytical rotors having at least two,and preferably more than two, radiation transmissive compartments toreceive samples. With such rotors, in each revolution a signal isobtained for each compartment and the problem is to separate out, andrecord if desired, the signal corresponding to just one compartment. Ina preferred embodiment, gating signals to select one of the compartmentsare obtained by sensing without contact with the rotor distinct portionscarried by the rotor and corresponding to respective compartments,whilst the compartment selected is defined or identified by sensing apredetermined angular position of the rotor by means of said surfaceportion of the first aspect of the invention.

More generally, according to a second aspect of the invention, there isprovided an analytical centrifuge for operation with analytical rotorswith at least two compartments to receive samples, the centrifugecomprising a compartment examining system by which radiation can bepassed through said compartments and the radiation transmitted throughthe compartments sensed and corresponding signals fed to a signal path,and sensing means for sensing without contact with the rotordistinctportions carried by the rotor and corresponding to respective rotorcompartments, these means being connected to supply signals to controlmeans of the examining system so that said signal path will carry asignal corresponding to the radiation passed through just one of thecompartments, the sensing means also being effective to sense apredetermined an gular position of the rotor to define the compartmentcorresponding to said signal on the signal path.

Thus, one can obtain from said signal path data relating to theradiation passed through one particular compartment regardless of theradiation passed through the other compartment or compartments.

The arrangement could be such that a signal will be produced in eachrevolution on each of two signal paths corresponding to respective onesof two compartments, the two signals being combined to produce a thirdsignal defining the difference between the radiation absorptionproperties of material in said two compartments. One of these twocompartments may therefore contain a reference medium.

As the sensing means is also operable to sense a predetermined angularposition of the rotor to define to which distinct portion, and thereforeto which compartment, the signal corresponds, the distinct portions canprovide substantially identical responses at the sensing means yet adistinction can still be made between the compartments. For example,with sensing means operating optically, the portions may all havesubstantially the same light-affecting property, which is different fromthe light-affecting property of adjacent portions carried by the rotorin order to obtain distinct, but similar, signals in respect of eachcompartment. However, the light-affecting properties could alternativelyalternate from one distinct portion to the next.

The track mentioned above in respect of the first aspect of theinvention can thus be utilised to sense a predetermined angular positionof the rotor, for example by sensing the leading or trailing edge of thesignal produced in accordance with the first aspect of the invention.

Thus, according to another aspect of the invention, the rotor carriestwo arcuate tracks one having a plurality of distinct portionscorresponding to respective compartments of the rotor and the otherhaving a portion of a length along a circular path centred on the rotoraxis which defines the maximum desired speed of rotation of the rotor.The latter track may then be used not only for overspeed protection butalso for the synchronisation of the multicompartment scanning inaccordance with the second aspect of the invention.

DESCRIPTION OF DRAWINGS For a better understanding of the invention andto show how the same may be carried into effect, reference will now bemade, by way of example, to the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of an analytical centrifuge;

FIG. 2 is a diagram representing reflective tracks carried on theunderside of the rotor of the centrifuge of FIG. 1;

FIGS. 3a and 3b show wave forms of signals generated by the tracks shownin FIG. 2;

FIG. 4 is a block diagram of the overspeed control circuit for thecentrifuge of FIG. 1;

FIGS. 5a and 5b are wave forms indicating the man net of operation ofthe circuit of FIG. 4;

FIG. 6 is a block diagram of a circuit for synchronising the opticalscanning in the centrifuge of FIG. 1; and

FIG. 7 is a diagram of the signals occurring in the circuit of FIG. 6.

FIG. 1 illustrates diagrammatically an analytical centrifuge comprisinga centrifuge motor 1 supplied via a variable frequency 3-phasesinusoidal inverter 2 for speed control of the motor. The motor shaft 3is releasably coupled to a rotor 4 mounted within a vacuum tightenclosure 5 coupled to a vacuum pump or pumps 6. The rotor 5 has aplurality, for example six, of compartments two of which are indicatedat 7. These compartments are closed top and bottom by light transmissiveclosures and are adapted to hold light transmissive cells containingmaterial to be analysed. This material will normally be in the form of asample suspended in a carrier liquid and this carrier liquid will becontained by itself in one cell, which will act as a reference cell.

The enclosure 5 has light transmissive windows 8 and 9 through which thecells may be viewed successively during rotation of the rotor 4. A lightgenerating system 10 is arranged to direct light upwardly into theenclosure 5 and through successive cells, and a photodetector 11 ispositioned to receive that portion of the light which has passed throughthe cells. The centrifuge is also equipped with two arrangements 12 and13 each containing a light source and a light sensor.

The light sources are arranged to direct light onto the lower surface ofthe rotor 4 and the light sensors are arranged to receive that lighthaving been reflected from the rotor 4.

FIG. 2 is a diagram showing the pattern of reflecting and substantiallynon-reflecting surface portions which are provided on the lower surfaceof the rotor 4. This pattern consists of two circular tracks concentricwith the axis of rotation of the rotor, the inner track 14 consisting ofa reflecting section 15 and a substantially non-reflecting section 16.The length of the section 15 is directly proportional to the desiredmaximum speed of rotation of the particular rotor. The arrangement 12comprises a light source 17 directing its light onto the track 14 and aphoto-detector 18 positioned to receive light reflected from this track.Accordingly, the photodetector 18 will produce a signal in eachrevolution of the rotor which has a time duration which is proportionalto the length of the section 15, and inversely proportional to'theactual speed of rotation of the rotor. This signal is illustrateddiagrammatically in FIG. 3b for a section 15 which extends for 270 aboutthe axis of rotation of the rotor 4.

The second track 19 comprises six equal-length reflecting sections 20spaced apart by six equal-length substantially non-reflecting sections21. The sections 20 have their centres on substantially the same radiias the centre lines of six respective compartments in the rotor. Thearrangement 13 comprises a light source 22 directing light onto thetrack 19 and a photo-detector 23 arranged to receive reflected lightfrom this track. The signal produced by the photo-detector 23 isindicated in FIG. 3a.

The signal produced by the photo-detector 18 and derived by means of thetrack 14 is utilised to prevent the rotor from being driven above itspredetermined maximum speed as defined by the length of the section 15.FIG. 4 indicates in diagrammatic form the overspeed control circuit. Inthis figure is shown the light sources 17 and 22 directing light via therotor 4 to the photo-detectors 18 and 23, which may be photomultipliers.The signals produced by the photomultipliers and indicated in FIGS. 3aand 3b are fed to amplifiers 24a and 24b. The output of amplifier 24b isconnected back to a lamp supply circuit 17a to vary the light level in asense tending to maintain the amplitude of the signal of FIG. 3asubstantially constant. The output of the amplifier 24a feeds a pulseduration comparator 25 and a differentiating circuit 26, which lattercircuit supplies a trigger pulse at the positive edge of the signal ofFIG. 3b to trigger a pulse generator 27. When triggered, the pulsegenerator 27 supplies a reference pulse B of predetermined duration tothe comparator 25. A signal at the output 28 of the comparator iseffective to cause disconnection of the supply to the motor 1 orotherwise to limit its speed. FIG. 5a illustrates the conditions at thecomparator whilst the rotor is being run up to speed. At A is indicatedthe pulse fed to the comparator via the amplifier 24a and at B isrepresented the reference pulse B produced by the pulse generator. Asindicated in this figure the pulse A has a longer duration than that ofpulse B, indicating that the rotor speed is less than the permissiblemaximum speed; Uner these conditions, there will be no signal at theoutput 28. When the rotor speed increases, the length of the pulse Afalls until it reaches that of the pulse B. Any further increase of therotor speed will further decrease the duration of the pulse Ato give thecondition illustrated in FIG. 5b, whereupon the comparator will issue anoutput signal at 28 which indicates that the rotor speed has increasedabove the maximum permissible speed. As indicated, this output signalwill cause deceleration of the motor 1, for example by positive brakingor merely by disconnecting its supply.

The amplifiers 24a and 24b also produce signals on lines 29a and 29b forsynchronising purposes in the circuit of FIG. 6 which controls theoptical scanning of the cells in the centrifuge rotor.

' FIG. 6 illustrates a stepping motor 30 driven by a pulse generator 31and stepping a rheostat 32 which supplies the 2: input of an x-yrecorder 33. The stepping motor 30 also controls the ultra-violet lightgenerator which supplies ultra-violet light through the cells of therotor 4. The generator 10 produces a beam of elongate cross-section ofultra-violet light, the length direction of the cross-section extendingat the cells in the peripheral direction in relation to the rotor axis.This beam is stepped radially along the rotor by means of the steppingmotor. The light from the generator 10 passes to a photomultiplier 11having passed through the rotor cells. Therefore, in each revolution 'ofthe rotor, having in the present example six cells, the photomultiplierwill produce six pulses relating to the respective cells and thesepulses must be separated from one another. For this purpose, the pulsesare fed, via an amplifier 34, to two signal channels 35 and 36. Thesechannels contain respective gating and holding circuits includinglow-pass filters to form the average of the pulses received. Eachcircuit is operated so as to process and pass-on a signal relating toonly one of the six pulses occurring in any one revolution of the rotor.

The gating and holding circuits 37 and 38 are controlled by a counterhaving three bistable stages 39, 40 and 41 the outputs of which areconnected to the circuits 37 and 38 via a decoder and respectivesixposition selector switch pairs 42 and 43. The setting inputs of thebistable stages are connected to the light sensor 23 via line 29b and amonostable circuit. The stages will therefore receive six pulses perrevolution. The reset inputs of the bistable stages are each fed fromthe line 29a of FIG. 4 via a monostable circuit and are thus fed withone pulse per revolution. As a result, in

each revolution of the rotor, the six fixed contacts of each selectorswitch of the pairs 42 and 43 will each receive one of six successivepulses from the counter 39, 40 and 41. The moment at which each of thesepulses occurs is the moment at which the corresponding one of the rotorcells is passing the scanning position of the ultra-violet scanningsystem 10 and' 11. The pulses occurring at points in the circuit of FIG.6 are illustrated in FIG. 7.

It will now be assumed that a reference cell is in the secondcompartment of the rotor as counted from a reference position defined bythe track 14 and as indicated in FIGS. 3a and 3b. Accordingly, theselector switch pair 43 will be positioned at its second position, asillustrated. As a consequence, the circuit 38 will be opened only duringthe time in which the reference cell is being scanned by theultra-violet scanning system and accordingly the signal path 36 willonly transmit a signal corresponding to that one of the six pulses fromthe photo-multiplier 11 which has originated from the reference cell.Let it also be assumed that for the present it is intended to monitorthe sample cell in the third position of the rotor. The selector switchpair 42 will be in its third position, as illustrated, whereby thecircuit 37, and thus the signal path 35, will be open to process onlythat one of the pulses from the photo-multiplier l 1 which hasoriginated from the sample cell in position 3.

The signals in signal channels 35 and 36 are combined so as to obtain asignal corresponding to the difference in optical density propertiesbetween the sample cell and the reference cell and this signal is fed tothe y input of the recorder 33. To obtain this difference, each signalchannel contains a circuit 44, which produces an output signalrepresenting the logarithm of its input signal, and leads to a circuit45 which forms a signal representing the difference between its inputsignals. A device 46 is connected between the circuit 45 and therecorder 33 to enable the scale of the recorder to be expanded andcontracted as desired and to enable the y-origin to be chosen at will.

Finally, it is to be noted that the pulses of FIG. 3a have a repetitionrate proportional to actual rotor speed and may thus be used to act uponthe inverter 2 to maintain the rotor speed substantially at apresettable speed.

I claim:

1. In a centrifuge operable with a variety of rotors, with e'ach rotorthere being associated a maximum speed of rotation defined by an elementcarried by a respective one of said rotors, the centrifuge having meansfor sensing said element to prevent increase in the speed of rotation ofsaid rotor when the maximum speed is reached, the improvement whichresides in said element being a surface portion having, along an annularpath centered on the axis of said rotor, a length defining the maximumspeed and a property along its length which distinguishes said surfaceportion from the remainder of said annular path; said sensing meansbeing arranged to sense said property of the surface portion withoutcontact with said rotor to produce a signal having a time duration whichis a function of said length; and means for sensing when the timeduration of the signal has fallen to a predetermined value.

2. The improvement in a centrifuge as claimed in claim 1, wherein saidproperty is a radiation-affecting property different from that of saidremainder of the annular path, the centrifuge comprising radiationdirecting means for directing radiation at said annular path, and saidsensing means being radiation sensitive for receiving the radiation fromsaid path and originating from said directing means.

3. The improvement in a centrifuge as claimed in claim 2, wherein saidradiation is optical radiation.

4. The improvement in a centrifuge'as claimed in claim 1, and comprisinga pulse generator for generating a pulse of predetermined duration,means for triggering said generator at an edge of the signal, and aduration comparator for comparing the durationof the signal with that ofthe pulse.

1. In a centrifuge operable with a variety of rotors, with each rotorthere being associated a maximum speed of rotation defined by an elementcarried by a respective one of said rotors, the centrifuge having meansfor sensing said element to prevent increase in the speed of rotation ofsaid rotor when the maximum speed is reached, the improvement whichresides in said element being a surface portion having, along an annularpath centered on the axis of said rotor, a length defining the maximumspeed and a property along its length which distinguishes said surfaceportion from the remainder of said annular path; said sensing meansbeing arranged to sense said property of the surface portion withoutcontact with said rotor to produce a signal having a time duration whichis a function of said length; and means for sensing when the timeduration of the siGnal has fallen to a predetermined value.
 2. Theimprovement in a centrifuge as claimed in claim 1, wherein said propertyis a radiation-affecting property different from that of said remainderof the annular path, the centrifuge comprising radiation directing meansfor directing radiation at said annular path, and said sensing meansbeing radiation sensitive for receiving the radiation from said path andoriginating from said directing means.
 3. The improvement in acentrifuge as claimed in claim 2, wherein said radiation is opticalradiation.
 4. The improvement in a centrifuge as claimed in claim 1, andcomprising a pulse generator for generating a pulse of predeterminedduration, means for triggering said generator at an edge of the signal,and a duration comparator for comparing the duration of the signal withthat of the pulse.